During normal use, contact lenses become soiled or contaminated with a wide variety of compounds that can degrade lens performance. For example, a contact lens will become soiled with biological materials such as proteins or lipids that are present in the tear fluid and which adhere to the lens surface. Also, by handling of the contact lens, sebum (skin oil) or cosmetics or other materials can soil the contact lens. These biological and external contaminants can affect visual acuity and patient comfort. Accordingly, it is important to remove any debris from the lens surface for continued comfortable use with a lens care solution that contains one or more cleaning components.
Ophthalmic compositions formulated as a lens care solution must also contain one or more disinfectant components. Presently, the two most popular disinfectant components are poly(hexamethylene biguanide), at times referred to as PHMB or PAPB, and polyquaternium-1.
As stated, PHMB is presently used in contact, lens care solutions. These PHMB-based care solutions represent a significant improvement in patient comfort and antimicrobial effectiveness compared to most other antimicrobial components. However, as with any antimicrobial component there remains a tradeoff between the concentration of the antimicrobial component in the solution and the comfort experienced by the patient. Due to its wide commercial acceptance, extensive efforts have been directed to improve the antimicrobial efficacy or the comfort level to the patient by chemically modifying PHMB.
An alternative approach to improving patient comfort has been the introduction of comfort agents or hydrating agents to the lens care solutions. For example, U.S. Pat. No. 7,135,442 describes the use of dexpanthenol in combination with the sugar alcohol, sorbitol. It is said that the dexpanthenol helps to stabilize or minimize the disruption of the aqueous lachrymal layer by surfactants present in the lens care solutions.
The application of fluorescein to the cornea and the subsequent subjective and qualitative interpretation of the observed response is an accepted and important diagnostic tool to assess the physiological status of the cornea surface. Clinicians are cautioned, however, not to extrapolate from the clear clinical significance of high intensity, gross staining associated with corneal lesions and disease down to the meaning of superficial punctate corneal staining. Superficial punctate patterns of fluorescein dye fluorescence are to be viewed differently from nonsuperficial coalesced injury-related staining based on their common characteristics (superficial, transient and asymptomatic). For an extensive background and review on this subject, one is referred to Ward, K. W., “Superficial Punctate Fluorescein Staining of the Ocular Surface”, Optometry and Vision Science 2008, 85(1) 1.
Beginning in the 1980's, with the growing market of contact lens use, the number of descriptive case studies of superficial punctate corneal staining has increased in the scientific literature. Although the precise mechanisms that control the depth and extent of the fluorescence signal associated with superficial punctate corneal staining remains unclear, the studies as a whole do provide scientific support that such staining does not reflect corneal injury or toxicity. In fact, both epidemiological and experimental evidence demonstrates a lack of correlation between superficial punctate corneal staining and the institution of corneal infections. Nevertheless, there have been a few reports that attempt to characterize the intensity of superficial punctate corneal staining at 2-hours with corneal toxicity, or imply that there exists a correlation between such staining and the institution of corneal infections. Again, these reports offer no scientific or clinical data to support such assertions.
To alleviate any such concerns in the lens care solution market, Applicants sought out and developed ophthalmic compositions that exhibit relatively low, superficial punctate corneal staining at 2 hours following placement of hydrogel contact lenses soaked with the compositions. In fact, head-to-head the ophthalmic compositions described herein meet or exceed the superficial punctate corneal staining profile of the leading lens care solutions presently on the market.